Java字符串拼接效率测试

测试代码：

public class StringJoinTest {
    public static void main(String[] args) {
        int count = 10000;
        long begin, end, time;

        begin = System.currentTimeMillis();
        testString(count);
        end = System.currentTimeMillis();
        time = end - begin;
        System.out.println("拼接" + count + "次，String消耗时间：" + time + "毫秒");

        begin = System.currentTimeMillis();
        testStringBuffer(count);
        end = System.currentTimeMillis();
        time = end - begin;
        System.out.println("拼接" + count + "次，StringBuffer消耗时间：" + time + "毫秒");

        begin = System.currentTimeMillis();
        testStringBuilder(count);
        end = System.currentTimeMillis();
        time = end - begin;
        System.out.println("拼接" + count + "次，StringBuilder消耗时间：" + time + "毫秒");
    }

    private static String testStringBuilder(int count) {
        StringBuilder tem = new StringBuilder();
        for (int i = 0; i < count; i++) {
            tem.append("hello world!");
        }
        return tem.toString();
    }

    private static String testStringBuffer(int count) {
        StringBuffer tem = new StringBuffer();
        for (int i = 0; i < count; i++) {
            tem.append("hello world!");
        }
        return tem.toString();
    }

    private static String testString(int count) {
        String tem = "";
        for (int i = 0; i < count; i++) {
            tem += "hello world!";
        }
        return tem;
    }
}

测试结果：

结论：

　　在少量字符串拼接时还看不出差别，但随着数量的增加，String+拼接效率显著降低。在达到100万次，我本机电脑已经无法执行String+拼接了，StringBuilder效率略高于StringBuffer。所以在开发过程中通常情况下推荐使用StringBuilder。

　　StringBuffer和StringBuilder的区别在于StringBuffer是线程安全的。